After the drilling of a borehole into the earth has been completed for the purpose of exploration and/or testing for oil, gas, water and/or other minerals, a casing formed of pipe sections is usually run into the borehole and cemented in place. The casing helps to stabilize the different strata that have been penetrated by the borehole and keeps the borehole in a condition that allows testing tools, completion tools, production equipment and the like to be lowered into and retrieved from the borehole.
In order to isolate the different fluid producing strata from each other, and to stabilize and anchor the casing within the borehole, the casing is usually cemented into place. The cement provides a bond between the various strata which have been penetrated and the pipe within the borehole. With the varied strata having different properties and subsurface formation pressures, it is frequently necessary to provide coverage of all these zones with cement in order to isolate them from each other. In deeper wells, it is necessary, and has become standard operating procedure in many areas, to cement the casing in the borehole at different depths, as it may not be necessary nor economically feasible to cement the entire length of the casing within the borehole. Techniques of cementing the casing in the wellbore at various depths is commonly referred to as stage cementing. Typically, such multiple stage cementing processes allow cementing in separate stages, starting at the bottom of the borehole and progressing in stages up to the surface.
There are currently several types of stage cementing tools and apparatus on the market. For example, U.S. Pat. No. 4,333,530 to Armstrong shows a multistage cementing apparatus. In the typical process, multiple stage cementing is accomplished by the use of cementing tools, which are placed in the casing at one or more locations in the hole. In the first stage of the cementing operation, cement is pumped to the bottom of the casing and up the annulus to the lowest cementing tool in the well, or some lesser elevation as desired. In the next stage of the operation, the lower portion of the casing string is closed off and cement is pumped through a valve in the stage cementing tool into the annulus and up to the next cementing tool in the well, or some lesser height. Multiple stages of cementing are completed in this manner up to the surface of the well.
During primary cementing operations, it is desirable that the casing string be rotated and/or reciprocated to enhance cement bonding between the casing and the borehole wall. If the casing is not rotated and/or reciprocated while the cement is being forced into the annulus, poor bonding is likely to result. During the first stage of cementing, the entire casing string can be rotated and/or reciprocated while the cement is pumped into the annulus. However, after the first stage of cementing is complete and the casing string is fixed in place, further rotation and/or reciprocation of the casing string generally becomes impossible.
A need exists for an improved stage cementing tool which renders the process of multiple stage cementing more efficient and effective. A need particularly exists to achieve the advantages of casing string rotation and/or reciprocation of the individual segment being cemented to insure the most effective bond between the segment and the borehole.